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BIOL 1840U (44)

Gastric Secretion

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BIOL 1840U
Peter Cheung

Gastric Secretion I. Stomach Anatomy a. Extends from LES to pyloric sphincter b. Anatomical areas: cardiac (near LES) fundus (lg. central region) pyloric antrum (end portion where mixing occurs (antral peristalsis)) c. Gastric Glands i. Corpus & fundic glands—contain chief cells (pepsinogen), parietal cells (HCl), & mucous cells ii. Pyloric glands—contain G cells (gastrin) & D cells (somatostatin) d. Cells i. Parietal cells—elaborate network of apical membranes ii. Mucous & Chief cells—secrete into lumen => secretory granules at apex iii. Endocrine cells—secrete into blood => secretory granules at base II. Gastric Secretions a. Gastric juice secreted at rate of 1-10 L/day i. Increased flow rate => increased [HCl] in gastric juice ii. pH varies in response to food buffers & parietal cell regulation b. Mucosal defenses against HCl i. High rate of HCl secretion usually followed by food buffer ii. Mucus is a diffusion barrier (protective) iii. HCO3 is secreted by mucous cells and partially retained in mucus barrier iv. HCl secretion is under strict feedback c. Pepsin secretion i. Secreted from chief cells as pepsinogen (zymogen), activated by HCl ii. 2 forms (Pepsinogen I & II) w/ similar results iii. lower pH => increasing activity (can autocatalyze activation at low pH) iv. Fxn—breaks up connective tissue & protein v. pH optima is in acid range; denatured irreversibly above pH 7 d. Intrinsic Factor i. High affinity & specificity for cobalamin (vitamin B12) facilitating absorption of vit B12 in ileum ii. Secreted by parietal cells iii. Lack of IF => malabsorption of Vit B12 => pernicious anemia III. HCl Secretion by Parietal Cells a. Up to 150 mM HCl manufactured in stomach b. “secreted” by ATPase: i. have ATP driven H/K exchanger (pumps H into cell from ESF & K out of cell into ESF) ii. H diffuses out of cell into lumen iii. Cl follows passively iv. See 1:1:1 ratio (H:K:ATP) c. Movemen
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